It is forbidden to demand payment after the Shemita year for loans given before the end of Shemita. If the borrower offers to pay the loan, the lender is obligated to say, "Meshamet Ani" ("I cancel"), announcing the debts annulment.
The Ben Ish Hai (Rabbi Yosef Haim of Baghdad, 1833-1909), in Parashat Ki-Tavo, writes that this Halacha applies even to borrowed goods. For example, if a person borrows a dozen eggs from a neighbor toward the end of Shemita, and after Rosh Hashanah he approaches the neighbor to pay for the eggs, the neighbor must refuse to accept the payment. The reason, the Ben Ish Hai explains, is that borrowing grocery items is akin to borrowing money: the borrower uses the goods however he likes, with the expectation that he will pay the value of those foods with something else. This situation is identical to a monetary loan, which is given so that the borrower can spend the money and the repay the debt with other money. Therefore, a debt incurred by borrowing goods also falls under the obligation of "Shemitat Kesafim" (the remission of debts after Shemita).
In light of this Halacha, the Ben Ish Hai recommends that people specifically make a point of lending goods to their neighbors before Shemita, in order to have the opportunity to fulfill this special Misva. One should approach his neighbor before Rosh Hashanah and offer to lend items such as flour or eggs, and then, when the neighbor comes after Rosh Hashanah to pay, the lender should declare, "Meshamet Ani," and thereby fulfill the Misva of "Shemitat Kesafim."
Summary: Just as the end of the Shemita year cancels all loans, it similarly cancels debts incurred by borrowing grocery items such as food. Thus, if a neighbor borrowed eggs, for example, from his neighbor toward the end of the Shemita year, once Rosh Hashanah comes the lender may not demand or accept payment.
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